The polyamide industry uses a whole range of monomers, mainly lactams, ω-amino acids and “diamine-diacid” couples, denoted by the number of carbons per amide contained in the repeating unit of the polyamide. Mention may be made, for example, of the following polyamides: PA 6, PA 6.6, PA 6.10, PA 7, PA 8, PA 9, PA 11, PA 12, PA 13.
These monomers are manufactured, for example, via a chemical synthesis route especially using as starting material C2 to C4 olefins, cycloalkanes or benzene, but also castor oil (PA 11), erucic oil or lesquerolic oil (PA 13).
Current developments in environmental matters are leading, in the fields of energy and chemistry, to the exploitation of natural raw materials originating from a renewable source being favored. This is why certain studies have been undertaken in order industrially to develop processes using fatty acids/esters as starting material for manufacturing these monomers.
This type of approach has few industrial examples. One of the rare examples of an industrial process using a fatty acid as starting material is that for the manufacture, from ricinoleic acid extracted from castor oil, of 11-aminoundecanoic acid, which is the basis for the synthesis of polyamide 11 having the brand name Rilsan®. This process is described in the book Les Procédés de Pétrochimie by A. Chauvel et al. published by Editions TECHNIP (1986). 11-Aminoundecanoic acid is obtained in several steps: methanolysis of castor oil, pyrolysis of the methyl ricinoleate to obtain methyl undecylenate, which is hydrolyzed, and the acid formed is subjected to a hydrobromination to give the ω-bromo acid, which passes via amination to 11-aminoundecanoic acid.
The main research studies have related to the synthesis of 9-aminononanoic acid, which is a precursor of Nylon 9, from oleic acid of natural origin.
As regards this particular monomer, mention may be made of the publication n-Nylons, Their Synthesis, Structure and Properties—1997, published by J. Wiley and Sons, chapter 2.9 of which (pages 381 to 389) is devoted to polyamide 9. This article summarizes the achievements and studies performed on the subject. Mention is made, on page 381, of the process developed by the former Soviet Union which led to the marketing of Pelargon®. Mention is also made therein, on page 384, of a process developed in Japan using oleic acid originating from soybean oil as starting material. The corresponding description makes reference to the book by A. Ravve Organic Chemistry of Macromolecules (1967) Marcel Dekker, Inc., part 15 of which is devoted to polyamides and mentions on page 279 the existence of such a process.
For a full picture of the prior art, mention should be made of the numerous articles published by E. H. Pryde et al. between 1962 and 1975 in—Journal of the American Oil Chemists Society—Aldehydic Materials by the Ozonization of Vegetable Oils, Vol. 39 pages 496-500; Pilot Run, Plant Design and Cost Analysis for Reductive Ozonolysis of Methyl Soyate Vol. 49 pages 643-648 and R. B. Perkins et al. Nylon-9 from Unsaturated Fatty Derivatives: Preparation and Characterization JAOCS, Vol. 52 pages 473-477. It should be noted that the first of these articles also makes reference on page 498 to prior studies performed by Japanese: H. Otsuki and H. Funahashi.
To summarize this prior art directed toward this type of synthesis of PA 9 from plant oils, the following simplified reaction mechanism applied to the maleic ester, extracted from the oils by methanolysis, may be described:
Reductive Ozonolysis:H3C—(CH2)7—CH═CH—(CH2)7—COOCH3+(O3,H2)→H3C—(CH2)7—CHO+OHC—(CH2)7—COOCH3 Reductive Amination:OHC—(CH2)7—COOCH3+(NH3,H2)→H2N—(CH2)8—COOCH3+H2Ofollowed by hydrolysis leading to the amino acid.
This route, which is very appealing as regards the reaction, nevertheless has a large economic drawback consisting of the production during the first step of pelargonic aldehyde, which is very difficult to upgrade, including in the polyamide industry.
Patent GB 741 739 describes, for its part, the synthesis of this same acid from oleic acid, but using the oleonitrile route. A similar route is mentioned in the article by R. B. Perkins et al. mentioned above, page 475.
The simplified reaction scheme of this process is as follows.H3C—(CH2)7—CH═CH—(CH2)7—COOH+NH3→H3C—(CH2)7—CH═CH—(CH2)7—CN+2H2OH3C—(CH2)7—CH═CH—(CH2)7—CN+(O3+H2O)→H3C—(CH2)7—COOH+CN—(CH2)7—COOHCN—(CH2)7—COOH+2H2→H2N—(CH2)8—COOH
The synthesis leads to pelargonic acid (or nonanoic acid) H3C—(CH2)7—COOH as by-product.
The Applicant has, for its part, developed processes for manufacturing such ω-amino acid monomers which especially use metathesis reactions. Mention may be made in this respect of patent applications WO 08/104 722, WO 10/055 273 and WO 10/089 512, which describe processes in which the terminal amine function of the ω-amino acid results from the hydrogenation of a nitrile function, introduced either by cross metathesis with acrylonitrile (WO 08/104 722) or by ammoniation of the acid function (WO 10/055 273 and WO 10/089 512) in the context of a process proceeding via an ω-unsaturated nitrile or a monounsaturated dinitrile.
The diacids are, for their part, obtained industrially according to various methods, but which all have certain drawbacks. A wide panorama of these methods is developed in Kirk-Othmer's encyclopedia, 4th Edition, vol. A8, pages 118-136. Methods by degradation, such as ozonolysis or oxidation, of plant unsaturated fatty acids may be distinguished therein.
The ozonolysis of oleic acid, petroselinic acid and erucic acid makes it possible to produce, respectively, diacids containing 9, 6 and 13 carbon atoms.
Another example is the cleavage of ricinoleic acid via the action of sodium hydroxide at a temperature above 180° C. This method used industrially makes it possible to obtain the diacid containing 10 carbon atoms. The same method applied to lesquerolic acid leads to the formation of a diacid containing 12 carbon atoms.
This method has the advantage of using renewable starting materials, but is limited essentially to the manufacture of the C10 diacid, since lesquerolic acid is still not widespread, and this method is therefore sparingly used.
It is also possible to obtain diacids from molecules of smaller sizes by using techniques that are variants of carbonylation.
Finally, mention may be made of the bacterial fermentation of paraffins, which is a well-known method that makes it possible to obtain numerous diacids of variable chain length. However, this method does not make it possible to obtain diacids with a chain length greater than 16 carbon atoms, since the melting point of the paraffins is then too high to allow them to be transformed. Another important drawback is that bacteria consume some of the paraffins to ensure their growth, leading to low yields and to the need to purify the products.
The ozonolysis of erucic acid and oleic acid is used industrially for the production of diacids containing 13 and 9 carbon atoms, respectively. This technique has several drawbacks. Specifically, in the case of production of the diacid containing 9 carbon atoms, the starting material is oleic acid. This is present in nature as a mixture with stearic acid (acid of the same chain length but saturated). Stearic acid cannot react during the ozonolysis. However, it has a boiling point close to that of the diacid containing 9 carbon atoms, which complicates its separation. It is thus necessary either to use a very pure oleic acid (which is consequently more expensive) or to use efficient but expensive separation techniques downstream of the oxidative cleavage process to isolate the diacid. Moreover, these oxidative cleavage processes generate as coproduct pelargonic acid—a saturated linear acid containing 9 carbon atoms—which is aimed at a very different market (lubricants, herbicides, etc.) from that of the polymers, whereas the diacids are aimed at the markets of polyamides, polyesters and solvents (esters). In this type of process, products and coproducts have different growth markets. Further, as one of the products has a low growth value or even a degrowth value, the economic value of the process and thus that of the other product is largely reduced. It is thus advantageous, when a product is obtained with a coproduct, to find applications that address the same markets.
The Applicant has, for its part, launched studies in this field, which especially use the metathesis reactions in the context of a multi-reaction process.
Patent WO 08/155 506 describes a process that consists, in a first step, in transforming by pyrolysis or ethenolysis the unsaturated fatty ester into ω-unsaturated fatty ester and then, in a second step, in subjecting the product thus obtained to a metathesis reaction, either homometathesis to obtain a compound of formula ROOC—(CH2)m—CH═CH—(CH2)m—COOR, or cross metathesis with a compound of formula R2OOC—(CH2)r—CH═CH—R3 to obtain an unsaturated compound of formula ROOC—(CH2)m—CH═CH—(CH2)r—COOR2, which will be transformed by hydrogenation into saturated compounds.
Patent WO 09/047 444 describes a process for synthesizing diacids or diesters from monounsaturated long-chain natural fatty esters, which consists, in a first step, in oxidizing by fermentation the natural fatty ester to a monounsaturated carboxylic diester and then, in a second step, in subjecting the product from the first step to cross metathesis with a compound of formula R2OOC—(CH2)x—CH═CH—R3 to obtain an unsaturated compound of formula ROOC—(CH2)q—CH═CH—(CH2)x—COOR2, which, by hydrogenation, can lead to the saturated compound.
In a known manner, cross metathesis consists in reacting, in the presence of a catalyst, two unsaturated molecules according to the following schematic reaction process:A1A2−C=C−B1B2+D1D2−C=C−E1E2A1A2−C=C−D1D2+A1A2−C=C−E1E2+B1B2−C=C−D1D2+B1B2−C=C−E1E2 
Such an equilibrated reaction naturally poses problems with a view to an industrial use. The presence of four reaction products when the two reaction compounds are added, which, by hypothesis, have not completely reacted, contributes toward forming a complex mixture.
A person skilled in the art is always seeking to influence the composition of the resulting reaction mixture by carefully choosing the respective amounts of the two reagents and also the structure of the reagent D1D2−C=C−E1E2 so that the products formed are readily separable from the medium, and especially separable in gaseous form, which also has the advantage of shifting the reaction equilibrium and thus increasing the amounts of reaction products. The difficulty lies in selecting reagents which do not interfere with the products, and which do not generate coproducts that are difficult to separate from the reaction products.
It should be noted, however, that the reaction is performed in the presence of a catalyst that is also active for homometathesis reactions. This means that, besides the reactions mentioned above, the reaction below also takes place:A1A2−C=C−B1B2+D1D2−C=C−E1E2A1A2−C=C−A1A2+B1B2−C=C−B1B2+D1D2−C=C−D1D2+E1E2−C=C−E1E2 
This implies that during a cross metathesis, the operator's reaction medium comprises ten potential products. To limit the number of potential metathesis products, it is possible in certain cases to limit the formation of certain by-products and/or to limit the chemical feasibility of certain reactions intervening during the metathesis. This may be done especially by choice of the coreagent and/or by a separation of certain compounds gradually as they are formed. For example, by selecting compounds containing a double bond that is terminal or close to the end of the chain, the reaction coproducts will be light (gaseous) olefins which will be spontaneously removed from the liquid reaction medium.
Added to these obstacles inherent in the actual reaction is a difficulty associated with the catalyst, which, besides its activity in metathesis, is also active in isomerization. It has been observed, in certain cases, that this isomerizing activity of the catalyst increases when its metathesis activity decreases. The metathesis catalyst deactivated for the metathesis reaction appears to become transformed into a species that is active for catalyzing isomerization reactions. Under these conditions, the catalyst “in the depletion phase” in the presence of the long-chained olefins of the charge or of the products brings about a shift of the double bond of the reagent and/or fatty acid product. This leads to mixtures of isomers and brings about the formation of a mixture of products having different chain lengths. Since these chain lengths are, however, very similar, their respective separations are particularly difficult.
When cross metathesis is used for the purpose of synthesizing a target product, for example A1A2−C=C−D1D2 in the preceding equation, this product will therefore be accompanied, where appropriate, by the other three compounds of the cross metathesis and also by certain compounds derived from homometathesis, which is a reaction that automatically accompanies the main reaction, but also mixtures of isomers of these compounds.
The aim of the present invention is to manufacture “pure” products rather than mixtures, and the aim is thus to provide a process in which the yield of target product is maximized and in which the coproduct(s) synthesized have a substantial added value and a sufficient degree of purity without it being necessary to apply sophisticated and thus expensive purification techniques. An aim of the present invention is also to provide a process in which the product and coproduct preferably address the same final market.
The Applicant has now found such a process for overcoming the preceding drawbacks and for producing both an ω-amino acid as main product and a pure long-chain diester/diacid as coproduct, or difunctional derivatives thereof such as acid (ester)-alcohols, all making it possible directly to manufacture monomers for the polymer industry. The process of the invention thus makes it possible to provide on the same site two starting materials that can be used for the same purpose, namely the manufacture of polymers, and better still in the same type of polymerization process.
Without wishing to be bound by any theory, the Applicant thinks that the isomerizing activity of the metathesis catalyst decreases during the homometathesis reaction of the fatty acid if the homometathesis reaction is performed concomitantly with a cross metathesis in the presence of an unsaturated nitrile coreagent, which makes it possible to achieve the surprising result obtained by the process of the invention.